Which gas is considered a toxic substance that binds to hemoglobin?

Carbon monoxide is a toxic gas that poses significant health risks because of its ability to bind to hemoglobin in the blood. Hemoglobin is the protein responsible for transporting oxygen throughout the body. When carbon monoxide is inhaled, it competes with oxygen for binding sites on hemoglobin, forming carboxyhemoglobin. This process reduces the blood's ability to carry oxygen to vital organs and tissues, leading to symptoms such as dizziness, confusion, and even loss of consciousness, depending on the concentration of carbon monoxide and the duration of exposure.

In contrast, carbon dioxide is a natural component of the atmosphere and is produced during respiration. It does not bind to hemoglobin in a harmful way like carbon monoxide does. Methane is a flammable gas primarily associated with fossil fuel extraction and does not have the same toxic effects on hemoglobin. Carbon disulfide is also a toxic substance with harmful effects, but it does not specifically bind to hemoglobin in the way that carbon monoxide does. Thus, carbon monoxide stands out as the gas with direct and harmful effects on the oxygen-carrying capacity of blood.